/Engine/Source/Runtime/AudioMixer/Public/AudioMixerBlueprintLibrary.h
Start recording audio.Byleaving the Submix To Record field blank, you can record the master output of the game.
static void StartRecordingOutput ( const [UObject](API\Runtime\CoreUObject\UObject\UObject) * WorldContextObject, float ExpectedDuration, [USoundSubmix](API\Runtime\Engine\Sound\USoundSubmix) * SubmixToRecord )